This invention is an improvement in the gas-tight flange coupling art, and has particular application with respect to high-vacuum and high-pressure flange joints.
All-metal flange joints for use in applications requiring high-temperature and/or frequent bake-out of an assembled joint are known to the prior art. In particular, U.S. Pat. No. 3,208,758 to M. A. Carlson et al., assigned to Varian Associates, Inc., discloses an all-metal flange joint in which a gas-tight seal between mating flanges is provided by the flowing of soft metal gasket material into an annular groove formed between the facing flange surfaces when the two mating flanges are pressed together.
In the flange joint disclosed in U.S. Pat. No. 3,208,758, the opposing flange faces were configured so that a soft metal gasket could be received in a recess provided therebetween when the flanges are pressed together. Corresponding annular ridges were provided on the opposing gasket faces to project into the recess so as to penetrate into opposite sides of a peripheral region of the gasket located in the recess. A portion of the gasket material was thereby caused to flow into an annular groove that formed the periphery of the recess between the opposing flange faces. This groove was dimensioned to have a volume larger than the volume of gasket material that could flow into the groove, therby preventing gasket material from completely filling the groove. If an excess of gasket material were permitted to enter the annular groove, the opposing flange faces would be pushed apart. Proper dimensioning of the groove served to provide a gas-tight seal in the nature of a compressed O-ring, which could withstand pressure differentials limited only by the tensile strength of the metal gasket.
With prior art flanges of the type described above, however, difficulty was encountered in disassembling the flange joint after a seal had been made. Typically, such prior art flanges were coupled by bolting the two opposing flanges together. Such bolting or other compressive coupling of the mating flange faces caused compression of the gasket disposed therebetween, and resulted in the extrusion of soft metal from the periphery of the gasket into an annular groove formed at the periphery of the recess between the opposing flange faces. When the mating flanges were subsequently unbolted in order to disassemble the joint, however, the metal gasket frequently remained stuck to one or the other, or to both, of the flange faces.
When a soft metal gasket has been severely compressed against the surface of a harder metal, a surface bonding phenomenon in the nature of a weld occurs. In addition, a frictional restraining force dependent upon the coefficient of friction of the soft metal gasket material with respect to the harder surface of the flange tends to oppose movement of the gasket away from the flange.
In the prior art, the tendency of the metal gasket to remain affixed to one or the other, or to both, of the mating flanges was not an insurmountable problem in disassembling the joint when sufficient leverage was possible for applying an external force to separate the flanges. If, after separation of the flanges, the soft metal gasket remained attached to one or other of the flanges, the gasket could usually be removed quite easily by a hand tool for prying the gasket away from the flange to which it was attached. However, with the recent proliferation of applications requiring mini-flanges (i.e. flanges having a seal diameter of less than about one inch), the inaccessibility of mini-flange gaskets to removal by hand-held pyring tools has become a significant problem. Also, with large-diameter flanges (e.g., diameters larger than 23/4 inches), difficulty has been encountered in disassembling flange joints because of the large external force required to separate the gasket from either one of the flange faces. In many applications, it is advantageous from a system design standpoint to locate flanged coupling ports in places that are relatively inaccessible; and hence, a flange joint that does not readily disassemble is a serious inconvenience.
What is needed, therefore, is an all-metal flange joint in which the gasket tends to break away from the mating flange faces when the joint is disassembled.